Internal combustion engines require a source of combustion air. A typical source for combustion air is air drawn from outside of the vehicle, which commonly includes particulate contaminants. An air cleaner including an air filter element is normally provided in the air induction system to capture these particulate contaminants before combustion air is delivered to the vehicle engine.
Air filters include filter media having relatively small pores for air flow that operate to inhibit the passage of undesired particulate contaminants. Since the presence of a filter media in the intake air stream acts to restrict air flow, air flow through the filter element necessarily produces a pressure differential or pressure drop between the filter element inlet and outlet surfaces (i.e. across the filter media). This air flow induced pressure drop produces undesirable deflection forces in the filter media of the filter element. These deflection forces are aligned with the air flow direction and, (for example) in panel type air filters, the deflection forces are typically normal to plane defined by the filter element media. The deflection forces tend to distort, deflect or “crown” the filter element. The thickness and material chosen for use as a filter media needs to have filter pores of sufficient size to pass the fluid stream while blocking passage of undesired contaminants. Generally the use of thinner rather than thicker filter media elements may be preferred so as to reduce the pressure drop across the filter.
Air filter elements may be made of pleated filter paper. Pleating the filter paper media increases the available filter surface area, while the pleats additionally serve to reinforce the filter media of the filter element against deformation or deflection due to air flow induced forces. In normal operating conditions this is usually sufficient.
In operation, the filter element is subject to deflection forces induced by airflow through the filter element and the resulting pressure drop across the filter element. These deflection forces may tend to deform the filter element. Accumulation of dust or dirt in the filter media tends to obstruct pores in the filter media and increase the pressure drop with an increase resulting deflection forces. Filter media may absorb water during operation, for example if operated in rainy or dense fog conditions. Water wets the filter media, obstructs pores in the media and may act to further obstruct air flow through the media with the resultant further increase in pressure drop and resultant deflection forces. It is highly desirable to strengthen the filter element against deflection forces to avoid damage to the filter and better secure reliable operation of the air induction system.